Optical characterisation of an eye or eye-related system is an important step in assessing the health of an eye and in diagnosing pathological changes.
Examination of an eye in order to optically characterise the eye may include visual examination of the anterior and posterior eye to assess the health of the eye and diagnose pathological changes. Examination may also include the quantification of optical and anatomical characteristics of the eye. This typically involves refractometry; that is, the determination of the optical power of portion or the entire optical path travelled by an interrogating ray. This may, for example, include mapping—or spatially resolving—refractive power over an area or surface of the eye-related system, which is sometimes referred to as wavefront aberrometry. Determination of the optical and characteristics of the eye may also include the determination of various measurements of the eye-related system, such as the length of the eye-related system (i.e. the distance from the anterior surface of the cornea to the anterior surface of the retina), the profile and/or thickness of the cornea, the pupil size, and the depth of the anterior chamber. Such measurements may be important for certain surgical procedures (e.g. lens replacement or ablative laser treatment).
Several commercial instruments for eye examination are available. These include slit lamp biomicroscopes, anterior segment and retinal OCT instruments, keratometers, autorefractors, flouro-photometers, ophthalmoscopes and low coherence length and thickness measurement instruments. All of these instruments are designed to make observations or measurements at a single position and at a single, usually central, field angle. If other parts of the eye, or different angles, are to be assessed, either the instrument needs to be rotated and repositioned or the patient has to turn the eyeball or head. This restricts the speed and repeatability with which such measurements/observations can be obtained.
One particular aspect of ocular examinations, where speed and repeatability is critical is the measurement of peripheral refraction. Auto-refractors to measure the lower order aberrations of the eye and Hartmann-Shack aberrometers for higher order aberration measurements are commonly in use to measure central, on-axis refraction and wavefront aberrations. Several methods had been described to modify current instruments to make them suitable for measuring peripheral refraction. These methods usually involve the patient rotating eye or head to fixate at targets which are off-axis to the observation angle. By moving the fixation target, several measurements can be obtained for various peripheral angles and directions. Typically, these measurements are taken sequentially, leading to inaccuracies due to fluctuating fixation, accommodation and alignment and to prolonged measurement time.
Patent publication number WO 2008/116270 A1 titled “Characterising eye-related optical systems” describes an instrument that can measure an eye's refraction at multiple field angles by scanning the measurement beam across the visual field of the eye. The method and instrument described in this application, however, has some limitations as it does not allow for sharp focus to be maintained between observations/measurements at different field angles, and the accuracy of measurements taken from reflected wavefronts and/or images is relatively limited.
It would be desirable to provide methods and/or system capable of characterising-eye related systems by taking measurements and/or making observations from multiple field angles. In addition, it would be desirable to be able to take measurements/make observations with a relatively high degree of accuracy and/or with a relatively short measurement time.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.